New charge-carrier blocking materials for high efficiency OLEDs

Adamovich, Vadim; Cordero, Steven R.; Djurovich, Peter I.; Tamayo, Arnold; Thompson, Mark E.; D’Andrade, Brian; Forrest, Stephen R.

doi:10.1016/j.orgel.2003.08.003

Cited by 349 publications

(183 citation statements)

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“…5 In addition, the performances of PHOLEDs are greatly affected by the charge transport and charge recombination in the light emitting layer ͑EML͒. [6][7][8][9][10] .The most efficient way to get high recombination efficiency in PHOLEDs is to balance holes and electrons in the emitting layer. 6,8,9,[11][12][13][14] It was reported by He et al that the efficiency of green PHOLEDs could be doubled using a double layer emitting structure.…”

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confidence: 99%

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High efficiency phosphorescent organic light emitting diodes using triplet quantum well structure

Kim

Jang

Hong

et al. 2007

Applied Physics Letters

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Light emission in phosphorescent quantum well structure which can confine excitons within an emitting layer was investigated. A multilayer quantum well structure which has a narrow triplet band gap host material sandwiched between wide triplet band gap host materials was designed, and device performances were studied. The multilayer emitting structure gave high efficiency of 47 cd/ A compared with 11 cd/ A of standard green devices. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2731435͔ Light emission in phosphorescent organic light emitting diodes ͑PHOLEDs͒ depends on the properties of the organic material in the devices. 1-4 In particular, the energy level of the organic material has a great influence on the light emission in PHOLEDs. Depending on the energy level of charge transport materials, host, and dopant, different mechanisms dominate the light emission and recombination in PHOLEDs. Charge trapping and energy transfer mechanisms have been known to be a light emission path for the host and dopant system. Charge trapping plays a main role in red and green PHOLEDs, and energy transfer is the major light emission path for blue PHOLEDs. 5 In addition, the performances of PHOLEDs are greatly affected by the charge transport and charge recombination in the light emitting layer ͑EML͒. [6][7][8][9][10] .The most efficient way to get high recombination efficiency in PHOLEDs is to balance holes and electrons in the emitting layer. 6,8,9,[11][12][13][14] It was reported by He et al. that the efficiency of green PHOLEDs could be doubled using a double layer emitting structure. 6 The use of an effective hole or exciton blocking layer could also enhance the recombination efficiency of PHOLEDs. 8,11 Other than these, host and dopant materials were found to have a great impact on the recombination efficiency of PHOLEDs. 9,[12][13][14] Another way to get high efficiency in OLED is to confine excitons inside an emitting layer using a multilayer quantum well structure. 15,16 There have been several reports about quantum well structure which can confine holes or excitons within an emitting layer. Qiu et al. improved quantum efficiency of tris͑8-hydroxyquinoline͒ aluminium ͑Alq 3 ͒ devices by 120% using a copper phthalocyanine/ N , NЈ-di͑1-naphthyl͒-N , NЈ-diphenylbenzidine ͑NPB͒ quantum well structure. 15 They also reported an Alq 3 /rubrene quautum well structure and exciton confinement in rubrene layer. 16 There was four times improvement of quantum efficiency using rubrene as a quantum well. However, there was no report about triplet quantum well structure with phosphorescent dopants in EML.In this work, a phosphorescent quantum well structure which can confine charges and excitons inside EML was developed to improve the efficiency of green PHOLEDs, and the performances of green PHOLEDs were correlated with the device structure.Device configurations used in this experiment were indium tin oxide ͑150 nm͒/N , , 4Ј-diamine ͑60 nm͒/NPB͑30 nm͒/EML͑30 nm͒/biphenoxy-bi͑8-hydroxy-3-methylquinoline͒ aluminum ͑Balq͒ ͑5 nm...

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confidence: 99%

“…5 In addition, the performances of PHOLEDs are greatly affected by the charge transport and charge recombination in the light emitting layer ͑EML͒. [6][7][8][9][10] .…”

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confidence: 99%

High efficiency phosphorescent organic light emitting diodes using triplet quantum well structure

Kim

Jang

Hong

et al. 2007

Applied Physics Letters

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“…4. The triplet energy level of DTBT (2.44 eV) is similar to that of Ir(ppy) 3 (2.42-2.46 eV) 13 and lower than that of BCP (2.5 eV), 2 so that the Ir(ppy) 3 triplet excitons within the emitting layer can be partially transferred to the DTBT and to a lesser extent to the BCP triplet state, and non-radiatively decay in the DTBT and BCP layers. Further improvement of quantum efficiency may be obtained if a material with high triplet energy and low HOMO level is used as the HBL.…”

Section: Amentioning

confidence: 74%

Silane- and triazine-containing hole and exciton blocking material for high-efficiency phosphorescent organic light emitting diodes

Kang

Lee²,

Park

et al. 2007

J. Mater. Chem.

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One of the important factors for high efficiency phosphorescent organic light-emitting devices is to confine triplet excitons within the emitting layer. We synthesized and characterized a new hole blocking material containing silane and triazine moieties, 2,4-diphenyl-6-(49-triphenylsilanylbiphenyl-4-yl)-1,3,5-triazine (DTBT). Electrophosphorescent devices fabricated using the material as the hole-blocking layer and N,N9-dicarbazolyl-4,49-biphenyl (CBP) doped with fac-tris(2-phenylpyridine)iridium [Ir(ppy) 3 ] as the emitting layer showed a maximum external quantum efficiency (g ext ) of 17.5% with a maximum power efficiency (g p ) of 47.8 lm W 21, which are much higher than those of devices using bathcuproine (BCP) (g ext = 14.5%, g p = 40.0 lm W 21 ) and 4-biphenyloxolate aluminium(III) bis(2-methyl-8-quinolinato)-4-phenylphenolate (BAlq) (g ext = 8.1%, g p = 14.2 lm W 21) as hole-blocking layers.

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“…Many effective methods have been reported to reduce the hole mobility and improve the balance of holes and electrons in the emitting layer (Troadec et al, 2002;Mori et al, 2008;Kim et al, 2005). 2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline (bathocuproine, BCP) was used in OLED and organic photovoltaic cell because of its multiple role as hole blocking (Adamovich et al, 2003;Kim et al, 2008;Tomova et al, , 2010, exciton-blocking layer Tripathi et al, 2008;Mori & Kato, 2007;Wu et al, 2003), electron transporting and buffer layer , or in combination with NPB in (NPB/BCP) n (n-number of layers) as hole-trapping layer ( Shi et al, 2006). In this work we present our results concerning the role of bathocuproine as hole blocking layer in OLED structure: ITO/HTL/EML/HBL/ETL/M.…”

Section: Bathocuproine As Hole-blocking Layermentioning

confidence: 99%